Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write.
In a magnetic hard disk drive, the head typically comprises a free layer, a spacer, a pinned layer, and an exchange layer. The free layer is the sensing layer that is passed over the surface of the data bits to be read. The free layer is free to rotate in response to the magnetic patterns on the disk. The spacer is a nonmagnetic layer that separates the magnetization of the free and pinned layers. The pinned layer is usually held in a fixed magnetic orientation by its proximity to the exchange layer, which is a layer of antiferromagnetic material that fixes the pinned layer's magnetic orientation.